Well-based vertical hall element with enhanced magnetic sensitivity

ABSTRACT

A vertical Hall element and method of fabricating are disclosed. The method includes forming a buried region having a first conductivity type in a substrate having a second conductivity type and implanting a dopant of the first conductivity type into a well region between the top surface of the substrate and the buried region. The buried region has a doping concentration increasing with an increasing depth from a top surface of the substrate and the well region has a doping concentration decreasing from the top surface of the substrate to the buried region. The method includes forming first through fifth contacts on the well region. First and second contacts define a conductive path and second and third contacts define another conductive path through the well region. The fourth contact is formed between first and second contacts and the fifth contact is formed between second and third contacts.

FIELD OF THE DISCLOSURE

Disclosed embodiments relate generally to the field of magnetic sensors.More particularly, and not by way of any limitation, the presentdisclosure is directed to a well-based vertical Hall element withenhanced magnetic sensitivity.

BACKGROUND

Vertical Hall elements, which detect a magnetic field lying in the planeof the integrated circuit in which the vertical Hall element is formed,can be formed in either a substrate region that has uniform, low dopantconcentration or in implanted wells. When the vertical Hall elements areformed in implanted wells, historically these Hall elements inherentlyhave low sensitivity to in-plane magnetic fields. Increases insensitivity are conventionally achieved by narrowing the well and/orwell contact region. However, such narrowing leads to undesirably higherelectrical resistance. Greater sensitivity without increased resistanceis desired.

SUMMARY

Disclosed embodiments add a buried layer beneath the well-based verticalHall element. The buried layer has the same conductivity type as thewell but a higher concentration. Properly engineered, this buried layerdraws biasing current deeper into the region of the well where there islower dopant concentration than near the surface. This region of lowerconcentration provides higher Hall effect sensitivity.

In one aspect, an embodiment of a method of fabricating a vertical Hallelement is disclosed. The method includes forming a buried region havinga first dopant of a first conductivity type in a substrate having asecond conductivity type opposite the first conductivity type, theburied region having a first doping concentration increasing with anincreasing depth extended from a top surface of the substrate;implanting a second dopant of the first conductivity type into a wellregion between the top surface of the substrate and the buried region,the well region having a second doping concentration decreasing from thetop surface of the substrate to the buried region; forming first, secondand third contacts on the well region, the first and second contactsdefining a first conductive path through the well region, the second andthird contacts defining a second conductive path through the wellregion; forming a fourth contact on the well region between the firstand second contacts; and forming a fifth contact on the well regionbetween the second and third contacts.

In another aspect, an embodiment of an integrated circuit is disclosed.The integrated circuit includes a substrate having a top surface and afirst conductivity type; a well region formed in the substrate, the wellregion being doped with a first dopant of a second conductivity typethat is opposite the first conductivity type and having a first dopingconcentration that decreases with an increasing distance from the topsurface of the substrate; a buried region formed under and in contactwith the well region, the buried region being doped with a second dopantof the second conductivity type and having a second doping concentrationthat increases with increasing distance from the well region; first,second and third contacts formed on the well region, the first andsecond contacts defining a first conductive path through the wellregion, the second and third contacts defining a second conductive paththrough the well region; a fourth contact formed on the well regionbetween the first and second contacts; and a fifth contact formed on thewell region between the second and third contacts.

In a further aspect, a vertical Hall element is disclosed. The verticalHall element includes a substrate having a top surface and a firstconductivity type; a well region formed in the substrate, the wellregion being doped with a first dopant of a second conductivity typethat is opposite the first conductivity type and having a first dopingconcentration that decreases with an increasing distance from the topsurface of the substrate; a buried region formed under and in contactwith the well region, the buried region being doped with a second dopantof the second conductivity type and having a second doping concentrationthat increases with an increasing distance from the well region; first,second and third contacts formed on the well region, the first andsecond contacts defining a first conductive path through the wellregion, the second and third contacts defining a second conductive paththrough the well region; a fourth contact formed on the well regionbetween the first and second contacts; and a fifth contact formed on thewell region between the second and third contacts.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings in which like references indicate similar elements. It shouldbe noted that different references to “an” or “one” embodiment in thisdisclosure are not necessarily to the same embodiment, and suchreferences may mean at least one. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

The accompanying drawings are incorporated into and form a part of thespecification to illustrate one or more exemplary embodiments of thepresent disclosure. Various advantages and features of the disclosurewill be understood from the following Detailed Description taken inconnection with the appended claims and with reference to the attacheddrawing figures in which:

FIG. 1A depicts a cross-section of a vertical Hall element according toan embodiment of the disclosure;

FIG. 1B depicts a layout of the vertical Hall element of FIG. 1A asviewed from above according to an embodiment of the disclosure;

FIG. 1C depicts a cross-section of a vertical Hall element according toan embodiment of the disclosure;

FIG. 2 depicts the operation of the circuit of FIGS. 1A-B in detecting amagnetic field in the plane of the integrated circuit;

FIG. 3A depicts a graph of the concentration of dopants versus depth fora prior art version of the vertical Hall element without a buried layer;

FIG. 3B depicts a graph of the concentration of dopants versus depth fora version of the vertical Hall element having the disclosed buriedlayer;

FIGS. 4A and 4B depict current density for a prior art version of thevertical Hall element without a buried layer;

FIGS. 4C and 4D depict current density for a version of the verticalHall element having a buried layer;

FIG. 5 depicts sensitivity to a magnetic field versus resistance for aseries of prior art vertical Hall elements and for an embodiment of thedisclosure;

FIGS. 6A-6I illustrate fabrication of the vertical Hall element of FIG.1A according to an embodiment of the disclosure;

FIG. 7 depicts a block diagram of an integrated circuit containing aHall element and associated circuitry; and

FIG. 8A depicts a generalized method of fabricating a vertical Hallelement according to an embodiment of the disclosure;

FIGS. 8B-8D depict additional details of a method for fabricating anintegrated circuit according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. In the following detaileddescription of embodiments of the invention, numerous specific detailsare set forth in order to provide a more thorough understanding of theinvention. However, it will be apparent to one of ordinary skill in theart that the invention may be practiced without these specific details.In other instances, well-known features have not been described indetail to avoid unnecessarily complicating the description.

Turning first to FIG. 1A, a cross-section of a vertical Hall element100A according to an embodiment of the present disclosure is shown. Inthis embodiment, the vertical Hall element 100A is formed in a p-typesubstrate 102. In the embodiment shown in this figure, a p-typeepitaxial layer 104 has been grown on substrate 102. N-type buried layer(NBL) 106 is formed at the junction of substrate 102 and epitaxial layer104 and extends into portions of the substrate 102 and the epitaxiallayer 104. Deep n-type well (DNWELL) 108 is formed over NBL 106 suchthat DNWELL 108 extends from the surface of epitaxial layer 104 to NBL106. As will be discussed in greater detail below, NBL 106 is moreheavily doped than DNWELL 108 and acts to increase the sensitivity ofthe vertical Hall element 100A. Isolation structure 112, which in oneembodiment can be implemented by shallow trench isolation (STI)structures, separates both the n-type contact regions 110 and the p-typecontact regions 111 from each other and can be topped with a nitridelayer 114, a first inter-level dielectric layer (ILD1) 116 and a secondinter-level dielectric layer (ILD2) 118. Vias 113, which couple contactregions 110, 111 to a first metal layer 115 and to a second metal layer117 complete the vertical Hall element 100A. In operation, specificcontact regions 110 will be coupled to additional circuitry in order tosense a magnetic field in the plane of the substrate. The five n-typecontacts are labeled C1-C5 in order to discuss their operation below.Although the implementation shown in FIG. 1A can be STI structuresbetween the n-type contact regions C1-C5, other implementations may haveother configurations between the n-type contact regions C1-C5 (e.g.,heavily doped p-type regions or thin oxide layers).

FIG. 1B depicts a layout of a vertical Hall element 100B as seen fromabove according to an embodiment of the present disclosure. In thisembodiment, an outer ring of p-type contacts 111 is formed around theouter perimeter of vertical Hall element 100B and is coupled to thelower rail (e.g., ground) to serve as further isolation for the verticalHall element 100B. A ring of metallization 120 is formed above the innerperiphery of vertical Hall element 100B. Contacts C1 and C5 are eachcoupled to the metal ring 120 and from there to terminal T1. Contact C3is coupled via terminal T3 to a power supply (not specifically shown)that can provide a current through vertical Hall element 100B. ContactsC2 and C4 are coupled via terminals T2 and T4 to a voltage detector (notspecifically shown), which can sense the voltage between C2 and C4.While the examples shown in the present application are of an n-typewell 108 and buried layer 106 in a p-type substrate 102, the use of aburied layer 106 below the well 108 of a vertical Hall element 100A canalso be implemented using a p-type well and buried layer in an n-typesubstrate. Additionally, although FIGS. 1A and 1B illustrate a verticalHall element that is part of an integrated circuit (IC) and thusrequires isolation from the other components of the IC, Hall element100A, 100B can also be implemented as a discrete component. In anembodiment as a discrete component, details of the substrate, well andburied layer remain the same, but contacts C1-C5 are coupled to externalpins for eventual connection to other components.

Operation of a vertical Hall element 200 according to an embodiment ofthe present disclosure will now be discussed with reference to FIG. 2.During the operation of vertical Hall element 200, a biasing circuit 210is electrically coupled to contacts C1, C3 and C5 to provide a biascurrent (I_(BIAS)) that passes through the vertical Hall element 200 asdepicted by the arrows, i.e., an input from biasing circuit 210 iscoupled to contact C3, which passes the current I_(BIAS) into DNWELL208, where the current splits and flows to contact C1 and contact C5,i.e., half of I_(BIAS) flows toward contact C5 along a path 202B andhalf of I_(BIAS) flows toward contact C1 along a path 202A. In otherwords, contacts C1 and C3 define a conductive path 202A through DNWELL208 and contacts C5 and C3 define another conductive path 202B throughDNWELL 208. The presence of NBL 206 draws I_(BIAS) deeper into DNWELL208 than would occur if NBL 206 were not present. It is noted that theconductive paths illustrated in the figures are not intended to conveyan exact location of the conductive path, but are provided forillustration only. When a magnetic field is provided in a direction thatemerges perpendicular to the plane of the drawing, as represented byreference numeral B, the magnetic flux lines from the magnetic fieldexert a force on the electrons flowing along current path 202A. Theforce deflects these electrons towards the surface of DNWELL 208 andcauses a negative charge to accumulate near contact C2. Similarly, themagnetic flux lines exert a force in the opposite direction on theelectrons flowing along current path 202B. Here the force deflects theelectrons away from the surface of DNWELL 208, causing a positive chargeto accumulate around contact C4. As the electrons traveling alongcurrent paths 202A, 202B are deflected in different directions, apotential difference is produced between contacts C2 and C4, with themagnitude of the potential difference reflecting the magnitude of themagnetic field. The potential difference between contacts C2 and C4 ismonitored using a voltage detector 212 that is electrically coupled toC2 and C4; the presence of a voltage difference between contact C2 andcontact C4 is used to detect the presence of a magnetic field.

Hall element 200 can also be operated with current I_(BIAS) flowing inthe opposite direction from the direction shown in FIG. 2 to detect amagnetic field whose direction is reversed from the illustration, i.e.,pointing into the image plane. In yet another variation, Hall element200 can be operated with current I_(BIAS) flowing between contact C2 andcontact C4 with the difference in voltage between either contact C1 andcontact C3 or else between contact C3 and contact C5 being used todetect the presence of a magnetic field into or out of the plane of theimage. The number and arrangement of contacts shown in this figure ismeant to be illustrative, rather than restrictive, as many differentnumber and arrangements of contacts can be employed.

FIG. 1C illustrates an alternate embodiment of a vertical Hall element100C that uses the disclosed buried layer. Vertical Hall element 100Chas been formed in substrate 102 and is similar to Hall element 100A,except that vertical Hall element 100C has six contacts, numberedC1′-C4′, C6A and C6B, rather than the five contacts shown in FIG. 1A. Inthis embodiment, the upper rail is coupled to contact C2′, while thecontact C6A and contact C6B are coupled together. Bias current(I_(BIAS)) is passed from contact C2′ to contact C4′ along two paths,one shown as a solid line through well region 108 and the other shown asa dotted line that passes from C2′ to C6A, through the metallizationlayer to C6B and from C6B to C4′. As in the earlier embodiment, thepresence of NBL 106 draws I_(BIAS) deeper into DNWELL 108 than wouldoccur if NBL 106 were not present. When a magnetic field is provided ina direction that emerges perpendicular to the plane of the drawing (notspecifically shown), a voltage difference develops between contact C1′and contact C3′. Changes to the voltage between contact C1′ and contactC3′ signal the presence of a magnetic field. As in the embodiment shownin FIG. 1A, reversing the flow of the biasing current can be used todetect a magnetic field directed into the plane of FIG. 1C. The Hallelement can also be operated with current between contact C1′ andcontact C3′, with the Hall voltage measured between contact C2′ andcontact C4′. The use of a buried layer beneath a well structure that ispart of a Hall element is not limited to the specific embodimentsdisclosed here.

FIGS. 3A and 3B compare the dopant profiles for a vertical Hall elementaccording to the prior art and the dopant profiles for the disclosedvertical Hall element according to an embodiment of the presentdisclosure. In both of FIGS. 3A and 3B, the X-axis shows distance fromthe surface of the substrate in microns and the Y-axis showsconcentration of the dopants per cubic centimeter. In FIG. 3A, curve 302represents the n-type doping for a deep n-well that does not have thedisclosed underlying n-type buried layer. As seen in FIG. 3A, theconcentration of dopants in the portion of deep n-well nearest thesurface is approximately 3×10¹⁶/cm³. At greater distances from thesurface, the concentration of dopants in the deep n-well drops toapproximately 1×10¹⁴/cm³ at the bottom of the well. Curve 304 representsthe p-type epitaxial layer doping, which appears lower near the deepn-well and then rises to approximately 1×10¹⁵/cm³ at a depth of 5microns. The presence of the p-n junction below the n-well appears toprevent the biasing current from moving deeper into the well wheresensitivity is greater.

In FIG. 3B, the doping profile 302 of the deep n-well 108 is the same asin the example shown in FIG. 3A. However, at the point deep n-well 108ceases to contribute to the doping profile, n-type buried layer 106begins contributing, as shown by curve 306. As one moves deeper from thesurface of the silicon, the doping of NBL 106 increases fromapproximately 5×10¹⁵/cm³ to approximately 9×10¹⁸/cm³ at approximately6.5 microns depth. Thus, while the doping concentration of the n-wellgenerally decreases from the top surface of the substrate to the buriedlayer, the doping concentration of the buried layer increases with anincreasing depth from the top surface of the substrate and from the wellregion. Therefore, rather than a p-n junction at the bottom of n-well108, which can repel electrons moving in the n-well, there is anincreasing concentration of dopant that can attract the electrons andallow the current through the n-well 108 to flow deeper into the wellwhere the sensitivity is increased. The doping of the NBL 106 should becarefully calibrated to ensure that electrons in deep n-well 108 areattracted, but not captured by the buried layer 106. It is importantthat the doping of NBL 106 is low near the deep n-well 108, otherwisesensitivity would be compromised. Additionally, a large differentialbetween the maximum concentration in the n-well and the maximumconcentration in the buried layer is desirable. In FIG. 3B, thedifferential is approximately 1:100. The differential can also be in therange between 1:10 and 1:1000 inclusive.

The measured effect of adding a highly-doped buried layer 106 beneaththe deep n-well 108 is shown in FIGS. 4A-4D. FIG. 4A depicts currentflow within a vertical Hall element according to the prior art (i.e.,with no n-type buried layer), with the region of highest current density402 outlined; FIG. 4B is an enlarged version of the current flow in FIG.4A. In at least one embodiment, the outlined region generally includescurrent density having a maximum value of 1.21×10⁵ A/cm². Note that thecurrent flow is all concentrated in the upper portion of the silicon.FIGS. 4C-4D depict current flow in a vertical Hall element when ahighly-doped buried layer is added; again FIG. 4D is an enlargement ofFIG. 4C. The outlined region 404 is again the region of highest currentdensity and includes current density having a maximum density of 1.26A/cm². As can be seen in FIGS. 4C and 4D, the presence of the highlydoped buried layer draws the current flow much deeper into the silicon,where the vertical Hall device is able to provide greater sensitivitywithout increasing the resistance, as previous attempts to improve thesensitivity have done. The region of current flow is much larger andmore effective. Notably, providing a buried layer underneath a verticalHall element that is not well-based would not have the same effect. In avertical Hall element that is constructed directly in a substrate orepitaxial layer and not in a well, the doping throughout the body of thevertical Hall element remains essentially the same; even if the currentwere pulled deeper into the element, there is no differential in dopingconcentration in the vertical Hall element itself to provide theincreased sensitivity.

FIG. 5 provides a graph 500 that illustrates a comparison of a presentlydisclosed embodiment with previous attempts to increase sensitivity. Thesensitivity of various vertical Hall elements, which is measured involts per ampere per Tesla, is plotted against resistance in ohms. Inprevious attempts to increase sensitivity, which are graphed with opencircles, increases in sensitivity tend to correlate, in a roughly linearmanner, with increases in resistance. However the disclosed embodiment,which is graphed with a closed circle, provides sensitivity that liesroughly in the middle of the embodiments lacking a buried layer whileproviding a resistance that is lower than all but one of the embodimentsthat lack a buried layer.

FIGS. 6A-6I illustrate various points during the process of fabricatingan integrated circuit having a vertical Hall element according to anembodiment of the present disclosure. In FIG. 6A, p-type substrate 102provides the starting material. An upper surface of substrate 102 isoxidized to form oxide layer 620 on the surface of substrate 102,followed by deposition of photoresist layer 622. In FIG. 6B, photoresist622 has been patterned to provide an opening in the region where then-type buried layer is desired, oxide layer 620 has been removed fromthis region, and an n-type dopant is being implanted into substrate 102.In one embodiment, the dopant is antimony, which is implanted at adosage of between approximately 8×10¹⁴/cm² to approximately 5×10¹⁵/cm²and energy of between approximately 60 KeV and 150 KeV. In oneembodiment, antimony is deposited at a dosage of 3.0×10¹⁵/cm² at 60 KeV.FIG. 6C illustrates the same region of substrate 102 after the dopanthas been implanted to form region 603 and any remaining photo resist hasbeen removed.

After the implantation is completed, oxide layer 620 is removed and anew oxide layer 624 is grown. As seen in FIG. 6D, an annealing processhas been performed to diffuse the dopant in region 603 to arrive atdiffused dopant region 603′ and to heal any damage to the substrate 102caused by the implantation. In one embodiment, the annealing process isperformed for 150 minutes at 550° C., for 120 minutes ramping from 550°to 1150° C., for 30 minutes ramping from 1150° to 1200° C., for 80minutes at 1200° C., for 50 minutes ramping from 1200° to 1150° C., for60 minutes ramping from 1150° to 1000° C., and for 100 minutes rampingfrom 1000° to 600° C.

Following the annealing process, oxide layer 624 is removed andepitaxial layer 104 is grown. As epitaxial layer 104 is grown, region603 is driven into epitaxial layer 104 to form buried layer 106, asillustrated in FIG. 6E. As also seen in FIG. 6E, oxide layer 628 hasbeen grown on the surface of epitaxial layer 104 and photoresist 630 hasbeen deposited in preparation of implanting deep well 108. As seen inFIG. 6F, photoresist 630 and oxide layer 628 have been patterned toexpose the region over buried layer 106 and the dopant for deep n-well108 is being implanted. In one embodiment, deep n-well 108 is implantedwith both phosphorus at a dose of 2.0×10^(11/)cm² at 2 MeV and arsenicat a dose of 3.0×10¹²/cm² at 160 KeV. This will be followed by strippingoxide layer 628 and photoresist 630, growing a new oxide layer 632 andannealing the wafer. In one embodiment, the annealing process isperformed for 35 minutes while ramping from 750° to 900° C., for 20minutes ramping from 900° to 1000° C., for 25 minutes ramping from 1000°to 1100° C., for 17 minutes ramping from 1100° to 1150° C., for 277minutes at 1150° C., for 80 minutes ramping from 1150° to 910° C., andfor 80 minutes ramping from 910° to 750° C.

Following the annealing process, photoresist 634 is deposited andpatterned to expose regions over deep n-well 108 where shallow trenchisolation is desired. Regions for the shallow trench isolation areetched, giving the structure illustrated in FIG. 6G. FIG. 6H illustratesthe process after the shallow trenches have been filled, formingisolation structures 112, which in this embodiment are STI structures.New oxide layer 636 has been formed and photoresist 638 has beendeposited in preparation for implanting n+ or p+ dopants into thecontact regions 110 within deep n-well 108 and the surrounding ring ofp-type contacts 111. It will be understood that the n+ and p+ implantsare performed in two separate operations. A first photoresist layer (notspecifically shown) is deposited and patterned and n-type dopants areimplanted; after the implantation of n-type dopants is completed, asecond photoresist layer (also not specifically shown) is deposited andpatterned and p-type dopants are implanted. In one embodiment, then-type contacts 110 within deep n-well 108 are doped with both arsenicat a dose of 1.0×10¹⁵/cm² at 50 KeV and with phosphorus at a dose of1.0×10¹⁴/cm² at 70 KeV. In one embodiment, the p-type contacts 111 aredoped with boron at a dose of 2.3×10¹⁵/cm² at 10 KeV. Further processingto provide inter-level dielectrics and metallization, as shown in FIG.6I are conventional and well known to one skilled in the art and are notdetailed herein.

FIG. 7 depicts a block diagram of an integrated circuit chip 700 thatincludes a Hall element 704 and additional circuitry. In thisembodiment, IC 700 includes biasing circuit 702, which provides thebiasing current to appropriate contacts of Hall element 704, which in atleast one embodiment is a vertical Hall element having a highly-dopedburied layer under a deep n-well that forms the vertical Hall element,and voltage detector 706, which monitors the contacts within the Hallelement 704 that are provided for voltage detection and interprets theresults to provide an indication when a magnetic field is near. One useof chip 700 is in automobiles, where the Hall element 704 and a magnetcan be used to indicate whether a door or trunk is open or closed andprovide an indicator light to the driver of the vehicle.

FIG. 8A depicts a generalized method (800A) for fabricating a verticalHall element, while greater details of a specific embodiment areprovided in FIGS. 8B-D. Method 800A begins by forming (805) a buriedregion that has a first dopant of a first conductivity type in asubstrate having a second conductivity type that is opposite the firstconductivity type. The buried region has a first doping concentrationthat increases with an increasing depth extended from a top surface ofthe substrate. In one embodiment, the buried region has an n-type dopingand the substrate has a p-type doping. A second dopant of the firstconductivity type is implanted (810) into a well region between the topsurface of the substrate and the buried region. The well region has asecond doping concentration that decreases from the top surface of thesubstrate to the buried region. First, second and third contacts areformed (815) on the well region. The first and second contacts define afirst conductive path through the well region, the second and thirdcontacts define a second conductive path through the well region. Duringoperation of the Hall element, these conductive paths carry the biasingcurrent. A fourth contact is formed (820) on the well region between thefirst and second contacts and a fifth contact if formed (825) on thewell region between the second and third contacts. During operation thefourth and fifth contacts provide a voltage difference that is used todetect a magnetic field.

FIGS. 8B-8D together depict additional details of method 800 offabricating a well-based vertical Hall element according to anembodiment of the present disclosure. Method 800B depicts details offorming the buried layer according to one embodiment and begins withimplanting (830) the first dopant into a predefined region of thesubstrate, e.g., to form region 603. The method continues with annealing(835) the substrate and diffusing the implanted dopant. Next, the methodgrows (840) an epitaxial layer on the substrate and drives the implanteddopant into the epitaxial layer to form the buried region. The epitaxiallayer has the same dopant type as the substrate, e.g., the secondconductivity type.

Method 800C provides further details regarding forming the contactsassociated with the Hall element and continues by forming (845) anisolation structure at the surface of the substrate. The isolationstructure defines openings through which the first, second, third,fourth and fifth contacts and a plurality of contacts having the secondconductivity type are formed. A third dopant having the firstconductivity type is implanted (850) through openings in a firstphotoresist layer to form the first, second, third, fourth, and fifthcontacts. Next, a fourth dopant having the second conductivity type isimplanted (855) through openings in a second photoresist layer to formthe plurality of contacts around an outside perimeter of the wellregion. In method 800D, the substrate is annealed (860). Method 800D canbe performed at several different points in the process, e.g.,subsequent to implanting the first dopant at element 830 and subsequentto implanting the second dopant at element 810.

Although various embodiments have been shown and described in detail,the claims are not limited to any particular embodiment or example. Noneof the above Detailed Description should be read as implying that anyparticular component, element, step, act, or function is essential suchthat it must be included in the scope of the claims. Reference to anelement in the singular is not intended to mean “one and only one”unless explicitly so stated, but rather “one or more.” All structuraland functional equivalents to the elements of the above-describedembodiments that are known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the present claims. Accordingly, those skilled in the artwill recognize that the exemplary embodiments described herein can bepracticed with various modifications and alterations within the spiritand scope of the claims appended below.

What is claimed is:
 1. A method of fabricating a vertical Hall element,the method comprising: forming a buried region having a first dopant ofa first conductivity type in a substrate having a second conductivitytype opposite the first conductivity type, the buried region having afirst doping concentration increasing with an increasing depth extendedfrom a top surface of the substrate; implanting a second dopant of thefirst conductivity type into a well region between the top surface ofthe substrate and the buried region, the well region having a seconddoping concentration decreasing from the top surface of the substrate tothe buried region; forming first, second and third contacts on a topsurface of the well region, the first and second contacts defining afirst conductive path through the well region, the second and thirdcontacts defining a second conductive path through the well region;forming a fourth contact on the well region between the first and secondcontacts; and forming a fifth contact on the well region between thesecond and third contacts.
 2. A method of fabricating a vertical Hallelement, the method comprising: implanting a first dopant into apredefined region of the substrate to form a buried region having afirst dopant of a first conductivity type in a substrate having a secondconductivity type opposite the first conductivity type; annealing thesubstrate and diffusing the implanted dopant, the buried region having afirst doping concentration increasing with an increasing depth extendedfrom a top surface of the substrate; growing an epitaxial layer on thesubstrate and driving the implanted dopant into the epitaxial layer toform the buried region, the epitaxial layer having the secondconductivity type; implanting a second dopant of the first conductivitytype into a well region between the top surface of the epitaxial layerand the buried region, the well region having a second dopingconcentration decreasing from the top surface of the epitaxial layer tothe buried region; forming first, second and third contacts on a topsurface of the well region, the first and second contacts defining afirst conductive path through the well region, the second and thirdcontacts defining a second conductive path through the well region;forming a fourth contact on the well region between the first and secondcontacts; and forming a fifth contact on the well region between thesecond and third contacts.
 3. The method as recited in claim 1 furthercomprising forming an isolation structure at the surface of thesubstrate, the isolation structure defining openings through which thefirst, second, third, fourth and fifth contacts and a plurality ofcontacts having the second conductivity type are formed.
 4. The methodas recited in claim 3 further comprising implanting a third dopanthaving the first conductivity type through openings in a firstphotoresist layer to form the first, second, third, fourth, and fifthcontacts.
 5. The method as recited in claim 4 further comprisingimplanting a fourth dopant having the second conductivity type throughopenings in a second photoresist layer to form the plurality of contactsaround an outside perimeter of the well region.
 6. The method as recitedin claim 5 wherein the forming a buried region comprises implantingantimony at a dosage of between approximately 8×10¹⁴/ cm² andapproximately 5×10¹⁵/cm² and energy of between approximately 60 KeV and150 KeV.
 7. The method as recited in claim 5 wherein the forming aburied region comprises implanting antimony at a dosage of approximately3×10¹⁵/cm² and energy of 60 KeV.
 8. The method as recited in claim 5further comprising, subsequent to implanting the first dopant, annealingthe substrate at temperatures that range from approximately 550° C. to1150° C. for a period totaling approximately 590 minutes.
 9. The methodas recited in claim 5 wherein implanting the second dopant comprisesimplanting phosphorus at a dosage of approximately 2×10¹¹/cm² and energyof 2 MeV and implanting arsenic at a dosage of approximately 3×10¹²/cm²and energy of 160 KeV.
 10. The method as recited in claim 9 furthercomprising, subsequent to implanting the second dopant, annealing thesubstrate at temperatures that range from approximately 750° C. to 1150°C. for a period totaling approximately 534 minutes.
 11. The method asrecited in claim 5 wherein implanting the third dopant comprisesimplanting arsenic at a dosage of 1×10¹⁵/cm² and energy of 50 KeV andimplanting phosphorus at a dosage of 1×10¹⁴/cm² and energy of 70 KeV.12. The method as recited in claim 5 wherein implanting the fourthdopant comprises implanting boron at a dosage of 2.3×10¹⁵/cm² and energyof 10 KeV.
 13. The method as recited in claim 2 further comprisingforming an isolation structure at the surface of the epitaxial layer,the isolation structure defining openings through which the first,second, third, fourth and fifth contacts and a plurality of contactshaving the second conductivity type are formed.
 14. The method asrecited in claim 13 further comprising implanting a third dopant havingthe first conductivity type through openings in a first photoresistlayer to form the first, second, third, fourth, and fifth contacts. 15.The method as recited in claim 14 further comprising implanting a fourthdopant having the second conductivity type through openings in a secondphotoresist layer to form the plurality of contacts around an outsideperimeter of the well region.
 16. The method as recited in claim 2wherein the forming a buried region comprises implanting antimony at adosage of between approximately 8×10¹⁴/cm² and approximately 5×10¹⁵/cm²and energy of between approximately 60 KeV and 150 KeV.
 17. The methodas recited in claim 2 wherein the forming a buried region comprisesimplanting antimony at a dosage of approximately 3×10¹⁵/cm² and energyof 60 KeV.
 18. The method as recited in claim 2 further comprising,subsequent to implanting the first dopant, annealing the substrate attemperatures that range from approximately 550° C. to 1150° C. for aperiod totaling approximately 590 minutes.
 19. The method as recited inclaim 2 wherein implanting the second dopant comprises implantingphosphorus at a dosage of approximately 2×10¹¹/cm² and energy of 2 MeVand implanting arsenic at a dosage of approximately 3×10¹²/cm² andenergy of 160 KeV.
 20. The method as recited in claim 2 furthercomprising, subsequent to implanting the second dopant, annealing thesubstrate at temperatures that range from approximately 750° C. to 1150°C. for a period totaling approximately 534 minutes.
 21. The method asrecited in claim 20 further comprising, subsequent to implanting thesecond dopant, annealing the substrate at temperatures that range fromapproximately 750° C. to 1150° C. for a period totaling approximately534 minutes.
 22. The method as recited in claim 14 wherein implantingthe third dopant comprises implanting arsenic at a dosage of 1×10¹⁵/cm²and energy of 50 KeV and implanting phosphorus at a dosage of 1×10¹⁴/cm²and energy of 70 KeV.
 23. The method as recited in claim 15 whereinimplanting the fourth dopant comprises implanting boron at a dosage of2.3×10¹⁵/cm² and energy of 10 KeV.
 24. A method of fabricating avertical Hall element, the method comprising: forming a buried regionhaving a first dopant of a first conductivity type in a substrate havinga second conductivity type opposite the first conductivity type, theburied region having a first doping concentration increasing with anincreasing depth extended from a top surface of the substrate;implanting a second dopant of the first conductivity type into a wellregion in an epitaxial layer on top of the substrate, between a topsurface of the epitaxial layer and the buried region, the well regionhaving a second doping concentration decreasing from the top surface ofthe epitaxial layer to the buried region; forming first, second andthird contacts on a top surface of the well region, the first and secondcontacts defining a first conductive path through the well region, thesecond and third contacts defining a second conductive path through thewell region; forming a fourth contact on the well region between thefirst and second contacts; and forming a fifth contact on the wellregion between the second and third contacts.
 25. A vertical Hallelement, comprising: a buried region having a first dopant of a firstconductivity type in a substrate having a second conductivity typeopposite the first conductivity type, the buried region having a firstdoping concentration increasing with an increasing depth extended from atop surface of the substrate; a well region, having a second dopant ofthe first conductivity type, between the top surface of the substrateand the buried region, the well region having a second dopingconcentration decreasing from the top surface of the substrate to theburied region; first, second and third contacts on a top surface of thewell region, the first and second contacts defining a first conductivepath through the well region, the second and third contacts defining asecond conductive path through the well region; a fourth contact on thewell region between the first and second contacts; and a fifth contacton the well region between the second and third contacts.
 26. A verticalHall element, comprising: a buried region having a first dopant of afirst conductivity type in a substrate having a second conductivity typeopposite the first conductivity type, the buried region having a firstdoping concentration increasing with an increasing depth extended from atop surface of the substrate; an epitaxial layer on a top surface of thesubstrate, the epitaxial layer having the second conductivity type; awell region between the top surface of the epitaxial layer and theburied region, the well region having a second doping concentrationdecreasing from the top surface of the epitaxial layer to the buriedregion; first, second and third contacts on a top surface of the wellregion, the first and second contacts defining a first conductive paththrough the well region, the second and third contacts defining a secondconductive path through the well region; a fourth contact on the wellregion between the first and second contacts; and a fifth contact on thewell region between the second and third contacts.